1. Field of the Invention
The invention relates generally to manually operable drain valves for liquid containers, and in particular to a drain valve assembly for attachment to the threaded drain opening of an automobile crankcase.
2. Description of the Prior Art
According to conventional practice, oil is drained from the sump of an automobile crankcase by removing a drain plug and allowing the oil to discharge by gravity flow into a drain pan. This procedure is best carried out with the automobile supported overhead on a hydraulic lift. The drain plug is a male threaded plug having an integral tightening head portion, with the diameter of the tightening head being larger than the plug portion and usually formed in a hexagon configuration for engagement by a wrench. Considerable torque must be applied to tighten or remove the drain plug. Anyone who has changed the oil in their automobile will confirm that the drain plug removal procedure usually results in a large amount of oil being splashed onto the wrench and onto the operator's hands, and sometimes onto the floor or ground. This situation can be extremely dangerous, especially if the oil is hot.
Moreover, the drain plug will be at the same temperature of the oil, and is thus difficult to handle by hand. The drain plug is small, and if dropped onto a hard surface, its threads can be damaged. It is likewise easy to drop the drain plug into the drain pan or onto the floor where it may roll away and become lost.
An additional problem in handling a conventional drain plug is the risk of cross-threading the plug or over-torquing the plug and stripping the drain hole threads as it is reinserted into the crankcase.
It is particularly difficult to remove the drain plug from the crankcase without the use of a hydraulic lift since the clearance between the crankcase and ground level is very small. Moreover, in some engine arrangements, the drain plug is in a relatively inaccessible location, which limits the stroke range of back-and-forth manipulations required for tightening or loosening the drain plug. It will be appreciated that the job of removing and reinserting the drain plug is complicated in such situations by the fact that the drain plug cannot be seen by the operator unless he is directly beneath it, and in some cases only with the aid of a light.